DEC H7260 PSU fault

Glen Slick glen.slick at
Thu Jan 25 19:16:35 CST 2018

On Thu, Jan 25, 2018 at 3:06 PM, Jules Richardson via cctalk
<cctalk at> wrote:
> Hi all,
> I mentioned this in the thread where I'd asked about basic Microvax II info,
> but it may have got lost in traffic...
> The machine's H7260 PSU is somewhat unwell - one of the internal +5/12V
> supplies appears to be healthy, but the other has outputs which are sitting
> at around 2.5V (both on the 5V and 12V rails) under a test load.

Previously you also said:

> OK, the top PSU of the pair in this machine appears to be healthy. The
> bottom one, however, sits at around 2.5V on both the +5V and +12V outputs.
> That's without any cards, and the card-cage fan / temperature sensor
> unplugged, i.e. just with my dummy loads in place, so it looks like that PSU
> has issues (oh, and I tried decoupling the PSU from the backplane and
> loading it via the drive connector, so it doesn't appear to be a backplane
> issue).

Looking here at page 107 of the maintenance print set, BA123-A Basic
Enclosure Power Harness Wiring Diagram

Did you disconnect the wiring harness from J10 completely? If you
disconnected the temperature sensor module or the card-cage door
interlock switch I would expect that the power supply might not
operate normally.

I forget what the card-cage door interlock switch does, whether it
prevents the power supply from fully powering up, or if the power
supply does fully power up but also turns the fans on full blast if
the card-cage door is open which disrupts the normal cooling airflow.
I would check what my BA123 does, but that would require too much
moving of stuff about at the moment to get working space around it.

More information about the cctalk mailing list